ABSTRACT Heart failure (HF) is major and growing public health problem especially in older women. Despite advances in the treatment of established HF, prognosis remains poor in the elderly, therefore preventive efforts are needed. Lack of physical activity (PA) is a potent prospective risk factor for HF; while increased levels of PA are associated with reduced risk of HF in observational studies, the evidence that maintaining high levels of physical activity or increasing PA in sedentary individuals reduces the risk of heart failure is not presently available. A novel PA pragmatic trial embedded within the Women's Health Initiative (WHI) entitled WHI Strong and Healthy trial (WHISH) has been recently funded and will evaluate whether increasing physical activity, reducing sedentary behavior and increasing muscle strength through resistance training will reduce the risk of atherosclerotic cardiovascular disease but not the important outcome of HF. WHISH-2-Prevent Heart Failure will evaluate the effect of this RCT on incident HF and HF burden (all heart failure hospitalizations and CVD death in those with antecedent HF) as well as perform dose-finding analyses. WHISH-2-Prevent Heart Failure will be the first, largest, and longest primary prevention exercise trial ever performed in the highest risk group for HF-elderly women. An imbedded accelerometer study will allow for a dose-finding analysis regardless of the RCT results using newly developed MET-equivalent indices for elderly women.